The present invention relates to the measurement of signals, and more particularly to a subjectively weighted noise measurement method for multiple video formats.
Noise measurement is important in analog video testing because noise can directly and indirectly cause visible degradation. The spectral distribution of noise at a given level is important for determining the perceived noise degradation in video. Because of this frequency sensitivity, standards were developed for filter specifications used in frequency weighting for noise measurements of video in standard definition television. However standards do not exist yet for filters in other video formats, such as high definition and computer video. The standard definition filter specifications are specified for a much lower bandwidth than the high definition and computer video formats. Simply using bandwidth ratios of new and old formats to scale the filter frequency parameters of the existing specification does not give the intended result.
CCIR Recommendation (Rec) 576-2 FIG. 22, reproduced as FIG. 1 herein inverted to show attenuation as opposed to insertion loss, specifies the insertion loss versus frequency of a “unified weighting” filter for subjective weighting of noise for NTSC video. Filters meeting this specification have been implemented in analog, digital and software forms.
What is required is a perceptually consistent method of weighting noise present in analog video and equivalent digital representations across multiple formats. In particular it is desired to have one method of measurement for standard definition as well as other formats including high definition and computer video with variable sample rates, not necessarily known a priori or related to the clock rate of the corresponding digital video.